1. Field of the Invention
The present invention relates to a shoulder anchor height adjusting apparatus for adjusting the height of a shoulder anchor by moving the shoulder anchor through which a longitudinal intermediate portion of a webbing is inserted, at an upper portion of a side wall of a vehicle in a vertical direction of the vehicle.
2. Description of the Related Art
In a three point seat belt for securing a passenger, one end of a webbing is wound up onto a retractor which is mounted at a lower portion of a side wall of a vehicle. Further, the other end of the webbing is anchored by an anchor plate secured to the lower portion of the side wall of the vehicle through a shoulder anchor which is positioned at an upper portion of the side wall of the vehicle. A tongue plate is slidably fitted to the webbing between the shoulder anchor and the anchor plate. The tongue plate engages a buckle apparatus so that the webbing secures the passenger to the seat. The webbing between the shoulder anchor and the tongue plate forms a shoulder webbing, and the webbing between the tongue plate and the anchor plate forms a wrap webbing.
In order to adjust the shoulder webbing so as to conform to the body of the passenger, there is provided a shoulder anchor height adjusting apparatus for adjusting the height of the shoulder anchor.
In the conventional shoulder anchor height adjusting apparatus, as shown in FIG. 7 (in which an upper direction of the vehicle is shown by the arrow marked UP), a rail 80 is disposed at the upper portion of the side wall of the vehicle. A slider 82 is provided on the rail 80. A shoulder anchor 84 is attached to the slider 82. The slider 82 is moved and guided along the rail 80 in a vertical direction of the vehicle. The shoulder anchor 84 is thereby moved in the vertical direction of the vehicle. A long bolt 86 serving as a feed screw is arranged at the upper portion of the side wall of the vehicle in an outward direction with respect to the slider 82 and in a transverse direction of the vehicle so as to have the vertical direction of the vehicle as its axial direction. The long bolt 86 is screwed into a nut 88 serving as a screw member. The nut 88 inwardly extends in the transverse direction of the vehicle. The extending end of the nut 88 engages an engaging hole 90 which is opened in the slider 82. The long bolt 86 is rotated and driven by a motor so that the nut 88 is moved in the vertical direction of the vehicle. The extending end of the nut 88 pushes up or draws down the slider 82 through the engaging hole 90 of the slider 82 so as to move the slider 82 in the vertical direction of the vehicle.
In the conventional shoulder anchor height adjusting apparatus, a webbing 92 is pulled so that a load is applied to the shoulder anchor 84 when the height of the shoulder anchor 84 is adjusted after setting the webbing. The load is applied to the extending end of the nut 88 via the engaging hole 90 of the slider 82. Accordingly, in the long bolt 86, angular moment is generated about a line in a longitudinal direction of the vehicle perpendicular to an axis of the long bolt 86. Due to this angular moment, frictional resistance between the long bolt 85 and the nut 88 become larger. Consequently, a larger rotational driving force is required to rotate the long bolt 85 thereby necessitating a large-sized motor. It also becomes necessary to enhance the strength of the nut 88 and the long bolt 85.
As a result, the overall apparatus is large in size and heavy in weight making for an increase in production cost.